The Vackan and K'da originally all sprung to life in my FASA gaming days, so they started out mostly TMP/Lost Era.
However, a lot of our (myself and Klytus') ideas for the ships and technology were later realised in TNG/DS9/Voyager in one shape or another, so they can easily be integrated into those eras too.
The K'da Dominion, for example could fire from any point of their hull to effectively cover 360 degrees in the XYZ axes - kinda like Federatiion phaser strips. They didn't rely on traditional style warp drives and could appear anywhere without much warning (a lot like Borg transwarp conduits). They also had 'relay stations' dotted about to assist with longer distances.
Since the Vackan themselves aren't much affected by beam-type weapons in hand to hand combat, their technology reflected this by using rapid fire / high yield missile systems instead. Consequently, their vessels are constructed to resist heavy bombardment in the form of partially regenerative ablative armour.
However, I think where people want to see them fit is best left to their own preferences.
MajorRacal